My wife and I are preparing to build a new house in Southern NJ. We are trying to be as "green" and enviromentally friendly as possible. I recently came across the possibility of receiving the panels of fiberglass doors (specifically the 2' x 3' portion of the panel removed to install the window in the door). The supply is virtually endless. Can anyone offer advice on using these panels to insulate under my basement slab. These ate 1-3/4" polyiso foam panels with fiberglass (door covering) on both sides, R value of 10. The giberglass may help prevent crushing of the foam under weight of the concrete. Additionally, I was thinking about using the panels for the entire house. By double framing my exterior walls, I can get about an R40 in the walls. Stagger the seams and maybe spray foam the edges adjacent to the studs to really seam the house envelope. Furthermore, by using TJI (or like I joists) in the cathedral ceilings, I can insulate between the webs, thus allowing the cord of the I beam to serve as a spacer to allow airflow under the sheathing. I can essentially insulate the house 40% above minimum insulation requirements for a savings of 80%.

Can anyone comment on using these panels? Are there any issues with building codes (I know every municipality is different, but does anyone have experience or precident with this?) Are there any enviro factors with this application. We were going to use foam sheets to insulate under the basement... what's the difference if any? If door (recessed) panels are used will there be a small air pocket (?) between panels, will this cause any problems with condensation? Am I just being too "green" or just cheap?

Essentially, I am using foam insulation panels (which I read about in all of the energy smart publications). However, instead of buying 4' x 8' x 2" sheets, I am using 2' x 3' x 2" fiberglass coated panels. Are there any enviro factors, both inside and outside? Do you know of any reasons tha this is not a good idea? Please help with any advice possible. THANK YOU

I don't think using the panels under a slab would be a problem. Although extuded polystyrene is water resistant, I don't know about the polyiso. A vapor barrier below it might take care of the issue. Standard foam doesn't crush if the proper density is specified for the application. A basement is probably the least critical application. Condensation under the slab is not critical, but there could be moisture that could saturate the insulation.
I see doing the other part of your proposal as problematic for practical and code reasons. Not saying it can't be done, but I wouldn't bother.